Lighting design and the design of luminaires, fixtures and other lighting systems is often constrained by the limitations of the illumination source. In many applications, it is not easy or perhaps not possible to achieve a desired lighting effect with conventional illumination sources. For example, fluorescent tubes are available in a relatively small variety of fixed lengths. Incandescent and halogen lamps, e.g., A19 lamps, PAR lamps, and the like also generally have fixed sizes. Furthermore, these lamps are available in a relatively small number of light intensity ranges. Solid-state illumination sources such as LEDs by themselves are relatively small, but are typically mounted on rigid printed circuit boards and may require significant heat-sinking and/or thermal management. Thus, for solid-state lighting, while unique printed circuit boards may be designed and constructed, this is a time-consuming and costly process that prohibits cost-effective manufacture of a wide range of systems having different geometries. Furthermore, all such illumination sources are rigid, precluding easy implementation in applications requiring curved or arbitrarily shape illumination sources.
Relatively uniform and homogenous illumination is also a typical goal for illumination applications. For example, in systems made up of multiple conventional lamps, the large size of each light source (lamp or bulb) often results in non-uniform illumination, particularly in regions between lamps. In addition, in systems having multiple in-line fluorescent tubes, the regions between lamps for the sockets may result in undesirable socket shadow. The smaller size of solid-state emitters such as LEDs permits closer spacing; however, the large numbers of LEDs required to achieve high spatial uniformity have conventionally been limited to very expensive systems, because of the relatively high cost of the large number of LEDs.
One approach to improving uniformity is to increase the optical mixing between the multiple discrete illumination sources. One way to do this is with a diffuser and a mixing chamber. The amount of homogeneity is related to the amount of diffusion and the size of the mixing chamber—larger chambers are required for high uniformity, larger size illumination sources, larger spacing between illumination sources and for high-efficiency diffusers (high efficiency means relatively high transmittance and thus relatively low mixing or diffusion). Thus, higher uniformity may be possible, but it comes at the expense of size and rigidity—such systems are not amenable to small systems or free-form systems or systems requiring customization, for example signage, back illumination of custom panels or signs, channel lettering, or custom-length fixtures. For example, a family of free-form luminaires (for example having different shapes and/or sizes) will often require a different circuit board, or a set of different circuit boards for each luminaire in the family. Piecing together a large number of custom circuit boards increases installation difficulty, and also increases cost and reduces reliability.
In other applications, it is necessary to tailor the length or layout or shape of illumination sources to a specific fixture or system length or shape in order to achieve constant and uniform illumination over the entire fixture. For example, linear luminaires, such as slot lights, cove lights, linear fixtures, and the like often require customization (e.g., length customization) to fit a specific area or room. This is typically not possible with fluorescent lamps, because these are generally manufactured only in several fixed and unchangeable lengths. One solution is to use multiple LEDs on a printed circuit board such as FR4 or metal-core printed circuit boards (MCPCBs). Multiple boards may be combined to form a limited number of combinations, but the smallest increment of length change is limited by the circuit board size. Using a shorter circuit board permits finer adjustment of length, but requires a large number of circuit boards and interconnects between circuit boards, which increases the materials and assembly expense and reduces reliability. Using a longer circuit board permits the use of a smaller number of circuit boards, but does not permit fine adjustment of the length.
Accordingly, there is a need for solutions that provide LED-based lighting systems having the ability to provide inexpensive and reliable length and shape customization with high illumination uniformity, high efficiency, and which are simple to install.